High-entropy ultra-high temperature ceramic (HE-UHTC) coatings and deposition methods thereof

ABSTRACT

High-entropy ultra-high temperature ceramics (HE-UHTC) coatings deposited on substrates, as well methods for depositing the HE-UHTC coatings on the substrates, are provided. An HE-UHTC electrode can be fabricated via spark plasma sintering (SPS) and then a thin coating of the HE-UHTC can be deposited in a precision-controlled manner on a substrate via an electro-spark deposition process.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. applicationSer. No. 17/842,330, filed Jun. 16, 2022, the disclosure of which ishereby incorporated by reference in its entirety, including all figures,tables, and drawings.

BACKGROUND

Ultra-high temperature ceramics (UHTCs) with melting points of greaterthan 3,000° C. are known for their intriguing combination of metal-likeproperties and ceramic-like properties, offering excellent stability attemperatures above 2,500° C. These materials are also recognized aspotential materials for thermal protection systems (TPSs) owing toproperties that are beyond the capabilities of other structuralmaterials. A new class of UHTCs, referred as high-entropy UHTCs(HE-UHTCs) has gained interest due to the remarkable improvement intheir thermo-mechanical properties over ordinary UHTCs.

BRIEF SUMMARY

Embodiments of the subject invention provide novel and advantageoushigh-entropy ultra-high temperature ceramics (HE-UHTC) coatingsdeposited on substrates, as well methods for depositing the HE-UHTCcoatings on the substrates. An HE-UHTC electrode can be fabricated viaspark plasma sintering (SPS) and then a thin (e.g., less than 100micrometers (μm)) coating of the HE-UHTC can be deposited in aprecision-controlled manner on a substrate (e.g., an electricallyconductive substrate) via an electro-spark deposition process. TheHE-UHTC coating provides thermal and wear protection for the substrateon which it is deposited. The substrate can be, for example, steel,graphite, carbide (e.g., silicon carbide (SiC) such as carbon/SiC(C/SiC)), titanium (Ti), Ti alloy, a nickel (Ni) substrate (e.g., aNi-based alloy or superalloy, such as an austeniticnickel-chromium-based superalloy), or a carbon/carbon (C/C) composite.

In an embodiment, a method for fabricating a coating of a ceramicmaterial on a substrate can comprise: performing an SPS process on apowder of the ceramic material to give an electrode; and depositing thecoating of the ceramic material on (e.g., directly on and in physicalcontact with) the substrate by performing an electro-spark depositionprocess using the electrode. The ceramic material can be an HE-UHTC(e.g., (TaNbHfTi)C) or an intermetallic carbide (e.g., MAX®). Thesubstrate can be an electrically conductive substrate (e.g., steel,graphite, a nickel-based alloy (e.g., INCONEL®), or a titanium-basedalloy). The method can further comprise, before performing the SPSprocess on the powder of the ceramic material, preparing the powder ofthe ceramic material by ball-milling raw powders of a plurality ofceramic components. Each ceramic component of the plurality of ceramiccomponents can be an ultra-high temperature ceramic (UHTC), and thepreparing of the powder of the ceramic material can compriseball-milling the raw powders such that the powder of the ceramicmaterial comprises an equimolar composition of the UHTCs (e.g., HfC,TiC, and (TaNb)C). The depositing of the coating of the ceramic materialcan comprise precision controllable, automated, layer-by-layerdeposition of the ceramic material. The coating of the ceramic materialon the substrate can have a thickness in a range of, for example, from0.1 μm to 30 μm. The substrate can be such that no pre-treatment wasperformed thereon before the depositing of the coating of the ceramicmaterial on the substrate. The coating of the ceramic material on thesubstrate can comprise no oxidation or phase transformation. The coatingof the ceramic material on the substrate can be thermally stable up to atemperature of at least 2,500° C.

In another embodiment, a compound can comprise: an electricallyconductive substrate; and a coating of an HE-UHTC (e.g., (TaNbHfTi)C)disposed directly on and in physical contact with the substrate. Thesubstrate can be, for example, steel, graphite, a nickel-based alloy, ora titanium-based alloy. The HE-UHTC comprising an equimolar compositionof at least two UHTCs (e.g., HfC, TiC, and (TaNb)C). The coating of theHE-UHTC can have a thickness in a range of, for example, from 0.1 μm to30 μm. The coating of the HE-UHTC can comprise no oxidation or phasetransformation. The coating of the HE-UHTC can be thermally stable up toa temperature of at least 2,500° C.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) shows images of high-entropy ultra-high temperature ceramic(HE-UHTC) coatings on different substrates (clockwise from top-left:steel; INCONEL® (austenitic nickel-chromium-based superalloy); titanium(Ti) alloy; and graphite). The scale bars are, clockwise from top-left,5 millimeters (mm), 5 mm, 10 mm, and 5 mm.

FIG. 1(b) shows image of HE-UHTC coatings along the shrouded inner-sideof turbine blades with irregular geometry. From left to right are a topview, a side view, and a view of the fitted part after coating. Thescale bar is 10 mm.

FIG. 2(a) shows a plot of intensity versus 2 theta (in degrees), showingan X-ray diffraction (XRD) for an HE-UHTC coating on a steel substrate.No phase transformation or oxidation occurred during the coatingprocess.

FIG. 2(b) shows a plot of intensity versus 2 theta (in degrees), showingXRD patterns for, from bottom curve to top curve, different raw powders(each with a “pow” subscript) of HfC, TiC, (TaNb)C, and (TaNbHfTi)C, anda spark plasma sintered (SPS) sample of (TaNbHfTi)C (subscript of“SPS”).

FIG. 3 shows a plot of intensity versus 2 theta (in degrees), showingXRD patterns for, from bottom curve to top curve, SPS HE-UHTC, agraphite substrate, and a HE-UHTC coating. No phase transformation oroxidation occurred during the coating process.

FIG. 4 shows energy-dispersive X-ray spectroscopy (EDS) images of anHE-UHTC coating on a steel substrate. The images, clockwise fromtop-left, show the selected coating area on the steel substrate, andthen elemental mapping of C—K, Ti—K, Mn—K, Ta-M, Hf-M, Nb-L, and Fe— Kshowing the composition of the HE-UHTC coating on the steel substrate.Absence of any oxide phase is reconfirmed with these images. The scalebar is 100 micrometers (μm).

FIG. 5(a) shows a scanning electron microscope (SEM) image of across-section of an HE-UHTC coating on a steel substrate. The HE-UHTCcoating is ultra-thin and crack-free. The scale bar is 0.5 μm.

FIG. 5(b) shows an SEM image of a cross-section of a MAX® (carbide)coating on a steel substrate. The MAX® coating is ultra-thin andcrack-free. The scale bar is 0.5 μm.

FIG. 6(a) shows an SEM image of a cross-section of an HE-UHTC coating ona steel substrate. This HE-UHTC coating is thicker than that shown inFIG. 5(a). The scale bar is 50 μm. The stress-relief cracking in theHE-UHTC coating is due to its increased thickness. This occurs due tovolume change in the rapid solidification of the melted HE-UHTC duringdeposition. An optimization of the applied power and speed of therotating applicator can eliminate the stress-relief cracking in theHE-UHTC coating. Though, even the stress-relief cracking in the HE-UHTCcoating show outstanding wear performance (see also FIG. 9 ).

FIG. 6(b) shows an SEM image of a cross-section of the HE-UHTC coatingon the steel substrate from FIG. 6(a). The image shows good bonding ofthe HE-UHTC coating with the steel substrate. The scale bar is 100 μm.

FIG. 7(a) shows an image of a precision controllable automatedelectro-spark applicator for depositing HE-UHTC coatings, according toan embodiment of the subject invention.

FIG. 7(b) shows an enlarged version of a portion of the electro-sparkapplicator from FIG. 7(a) (see the arrow in FIG. 7(a)), depicting arotating applicator and an HE-UHTC electrode.

FIG. 8(a) shows an optical image of a Vickers' indent at 25 g force(g=9.8 meters per second squared (m/s²)) on an HE-UHTC coating (hardnessof 11 gigaPascals (GPa) to 14 GPa). The scale bar is 50 μm.

FIG. 8(b) shows an optical image of a Vickers' indent at 25 g force on asteel substrate (hardness of 2.5 GPa-3 GPa. The scale bar is 50 μm.Considered together with FIG. 8(a), it can be seen that hardnessimproved over 4.5 times with the HE-UHTC coating (even at a coatingthickness of about 25 μm).

FIG. 9 shows an optical image (upper portion of figure; scale bar is 50μm) of scratch testing that was performed to test wear resistance of anHE-UHTC coating at a constant load of 10 Newtons (N) and scratch lengthof 4 mm, along with coefficient of friction (COF) and acoustic emission(AE) data (middle portion of figure). The lower portion of the figureshows an optical micrograph of the overall scratch showing less damageon the HE-UHTC side than the steel substrate at a constant load of 10 N.The HE-UHTC coated region has a lower COF (0.40) than the steelsubstrate (0.65), which is an indication of an escalation in thetolerance towards wear damage.

FIG. 10(a) shows an image of a MAX® coating on a steel substrate. Thescale bar is 5 mm.

FIG. 10(b) shows an image of a MAX® coating on an INCONEL® substrate.The scale bar is 5 mm.

FIG. 11 shows a plot of intensity versus 2 theta (in degrees), showingan XRD pattern for a MAX® coating on a steel substrate. No phasetransformation or oxidation occurred during the coating process.

FIG. 12 shows EDS images of a MAX® coating on a steel substrate. Theimages, clockwise from top-left, show the selected coating area on thesteel substrate, and then elemental mapping of C—K, Al—K, Ti—K, Fe—K,and Mn—K showing the composition of the MAX® coating on the steelsubstrate. The scale bar is 20 μm.

DETAILED DESCRIPTION

Embodiments of the subject invention provide novel and advantageoushigh-entropy ultra-high temperature ceramics (HE-UHTC) coatingsdeposited on substrates, as well methods for depositing the HE-UHTCcoatings on the substrates. An HE-UHTC electrode can be fabricated viaspark plasma sintering (SPS) and then a thin (e.g., less than 100micrometers (μm)) coating of the HE-UHTC can be deposited in aprecision-controlled manner on a substrate (e.g., an electricallyconductive substrate) via an electro-spark deposition process. TheHE-UHTC coating provides thermal and wear protection for the substrateon which it is deposited. The substrate can be, for example, steel,graphite, carbide (e.g., silicon carbide (SiC) such as carbon/SiC(C/SiC)), titanium (Ti), Ti alloy, a nickel (Ni) substrate (e.g., aNi-based alloy or superalloy, such as an austeniticnickel-chromium-based superalloy), or a carbon/carbon (C/C) composite.

HE-UHTCs are typically made from a combination of a plurality (e.g.,two, three, four, five, or six, or more) of UHTCs in equimolarcomposition. Due to mutual solubility, a complete solid-solutionsingle-phase is formed as the HE-UHTC. HE-UHTCs possess exceptionallysuperior mechanical, oxidation, and erosion resistance as compared toconventional UHTCs. No related art technology exists for depositingHE-UHTC coatings on a substrate (e.g., to thermally protect astructure).

The related art focuses on processing and characterizing bulk HE-UHTC.However, the use of bulk ceramics in large and hot structures such aswing edges and nose cones is limited due to the intrinsic brittlenessand high density of these materials. Embodiments of the subjectioninvention make innovative applications of HE-UHTCs (e.g., HE-UHTCcoatings) possible. Preparation of HE-UHTC coatings on fiber-reinforcedcomposites (C/C, C/SiC), graphite, and Ni-based superalloys used formanufacturing critical components (e.g., for gas turbine engines and/orshipboard propulsion units) is a logical choice for improving theoxidation and ablation resistance in high temperature and oxygencontained environments. HE-UHTC coatings over can translate intoenormous savings of dollars per pound (e.g., of payload-to-orbit forrockets).

Related art coating methods for conventional UHTCs have a low content ofUHTC phases, high oxide content, and weak bonding with the substrate(see also, e.g.; Shirani et al., ZrB₂—SiC—WC coating with SiC diffusionbond coat on graphite by spark plasma sintering process, CeramicsInternational, 43, 14517-14520, 2017; which is hereby incorporated byreference herein in its entirety). Processing methods for depositingcoatings include sputter deposition, electroplating, electron beamirradiation, liquid precursor method, slurry coating, pack cementation,and chemical vapor deposition (CVD). In particular, pack cementation,CVD, plasma spray, and slurry sintering can be used to deposit UHTCcoatings. However, no related art technology exist to deposit HE-UHTCcoatings. The key issues with ceramic coatings on substrates (e.g., C/Ccomposites, graphite, Ti-based alloys) are adherence, continuity, andphase transformation (oxide phase formation) to resist delaminationduring extreme thermal excursions. No process exists in the related artto overcome these challenges to be able to deposit HE-UHTC coatings on asubstrate. Processes of embodiments of the subject invention overcomethese challenges while being simple so that coatings can be madereproducibly and reliably on various substrates (e.g., graphite, Ti,INCONEL® (austenitic nickel-chromium-based superalloy), and steel). Asimple electro-spark deposition process can be used.

Embodiments of the subject invention provide HE-UHTC coatings to protectstructural components from thermal and wear degradation. An HE-UHTCelectrode can be fabricated via SPS, and then thin (e.g., less than 100μm) HE-UHTC coatings can be deposited on an electrically conductivesubstrate via an electro-spark deposition process. The deposition can beperformed in a precision-controlled matter. FIGS. 7(a) and 7(b) showimages of a precision controllable automated electro-spark applicatorthat can be used for the electro-spark deposition process.

In an embodiment, electrode preparation can comprise mixing (e.g.,mixing by ball-milling) powders (e.g., raw powders) of the components ofthe HE-UHTC (e.g., tantalum (Ta), niobium (Nb), hafnium (Hf), and/or Ti,in a carbide (e.g., (Ta,Nb,Hf,Ti)C)) or other coating material (e.g.,MAX® carbide (e.g., TiAlC or Ti₂AlC)). After mixing the powders, SPS canbe performed on the mixed powders to form the electrode. A depositionmachine, such as a portable electro-spark deposition device (see FIGS.7(a) and 7(b)) can be used for depositing the coating on an electricallyconductive substrate using the prepared electrode in an electro-sparkdeposition process. If the prepared electrode is an HE-UHTC electrode,the coating will be an HE-UHTC coating. The coating can be anultra-thin, lightweight HE-UHTC (or other coating material) coating(e.g., a carbide coating) to increase oxidation resistance and extendthe service life of critical components made of materials such asheat-resistant metallic alloys and/or graphite.

The deposition processes of embodiments of the subject invention areapplicable to not just HE-UHTCs but also any other electricallyconductive ceramics including monolithic UHTCs (and any electricallyconductive substrate). For example, intermetallic carbide (MAX® phaseTi₂AlC) coatings can also be deposited to provide long-termhigh-temperature strength and resistance to oxidizing gas fluxes forcritical structural components of gas turbine engines, propulsion units,and other substrates (e.g., graphite, C/C, and C/SiC substrates).

The thickness of the deposited coating can be, for example, any of thefollowing values, about any of the following values, at most any of thefollowing values, at least any of the following values, or within arange having any of the following values as endpoints (all values are inμm): 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170,180, 190, 200, 225, 250, 275, 300, 350, 400, 450, or 500. For example,the thickness of the deposited coating can be less than 100 μm, such asfrom 0.1 μm to 30 μm (e.g., about 25 μm).

Embodiments of the subject invention provide ultra-thin, light-weightHE-UHTC and other carbide coatings on various substrates, including butnot limited to graphite, metal, and alloys (e.g., steel, Ti alloys, andnickel alloys (e.g., INCONEL®)), which are well-adhered, wear-resistant,and thermally stable. These coatings can also be applied to additivelymanufactured (AM) parts such as turbine blades as protection againsthigh-temperature (e.g., greater than 2,500° C.) erosion. The coatingsadhere well to the substrate with negligible heat affected zone. Noprior treatment or pre-treatment (e.g., polishing, heat-treatment,functionalization, pre-heating, or plasma treatment) of the substrate isrequired for enhancing coating deposition and adherence. The HE-UHTCshows excellent bonding irrespective of the substrate type (e.g.,metals, alloys, and graphite). The coating can be deposited withprecision control using a robotic system, and it can also be used forsurface texturing on ceramic substrates like conventional UHTCs toimprove their solar absorbance properties.

Embodiments of the subject invention have many advantages over relatedart coatings, including: no pre-treatment of the substrate (e.g.,polishing, heat-treatment, functionalization, pre-heating, or plasmatreatment) is required; the coatings are applicable to any electricallyconductive substrate (see also FIGS. 1(a) and 1(b)); the coatings showgood chemical compatibility and adherence on the substrate (see alsoFIGS. 5(a), 5(b), 6(a), 6(b), 8(a), and 8(b)); and no oxide phase ispresent in the coating (see also FIGS. 2(a), 2(b), 3, and 4).

Embodiments of the subject invention provide HE-UHTC coatings onmetallic and graphite substrates (see, e.g., FIGS. 1(a) and 1(b)),including on substrates with irregular geometries (see, e.g., FIG.1(b)). No phase transformation or oxidation is present in the HE-UHTCcoating region, leading to thermal stability of the coatings up to itsmelting temperature (e.g., about 3,000° C. or higher; see also, e.g.,FIGS. 2(a), 2(b), 3, and 4). The deposition can be precisioncontrollable, automated, layer-by-layer deposition (see also, FIGS.5(a), 5(b), 6(a), 6(b), 7(a), and 7(b)). The thickness of the HE-UHTCcoating can be in a range of from, for example less than 1 μm (e.g., 0.1μm) to 25 μm or more (e.g., 30 μm). Strong bonding is present betweenthe substrate and the HE-UHTC coatings (see also, e.g., FIG. 6(b)), andthe HE-UHTC coatings can be ultra-hard and wear-resistant (see also,e.g., FIGS. 8(a), 8(b), and 9). Embodiments of the subject invention canallow for surface texturing/patterning on various substrates, includingUHTCs, HE-UHTCs, and MAX® (see engraved texts “PFL” with HE-UHTC″ inFIG. 1(a) and “FIU” with MAX® in FIG. 10(a)) in a precise manner (e.g.,to tailor the solar absorption properties). The fabrication process isapplicable to other electrically conductive ceramics, including forexample monolithic UHTCs and intermetallic carbides (e.g., MAX® carbide)(see, e.g., FIGS. 5(b), 10(a), 10(b), 11, and 12).

Coatings of embodiments of the subject invention (e.g., HE-UHTCcoatings) can be used in various engineering applications, including inthe energy, automotive, and aerospace sectors. For example, HE-UHTC (andother ceramic) coatings can be used: in turbine applications (e.g., onablative seals and/or complex components to provide corrosion anderosion protection in severe environments such as hot/corrosive gas andsand erosion in military turbines); on agricultural tools (e.g., onsubsurface harvesting and/or cutter blades); in the nuclear industry(e.g., on nuclear graphite for high-temperature reactors (HTRs) and/oras burnable neutron absorber coatings); in the automotive industry(e.g., on valves (e.g., Ti valves) for racing engines); in aero-engines;as high-temperature thermal insulation; as high-temperature solarabsorption and/or receivers; in concentrated solar power (CSP)applications; in thermo-electric conversion; and/or in a spacepropulsion system (e.g., hypersonic vehicles, thrust chambers, and/orrocket nozzles).

The transitional term “comprising,” “comprises,” or “comprise” isinclusive or open-ended and does not exclude additional, unrecitedelements or method steps. By contrast, the transitional phrase“consisting of” excludes any element, step, or ingredient not specifiedin the claim. The phrases “consisting” or “consists essentially of”indicate that the claim encompasses embodiments containing the specifiedmaterials or steps and those that do not materially affect the basic andnovel characteristic(s) of the claim. Use of the term “comprising”contemplates other embodiments that “consist” or “consisting essentiallyof” the recited component(s).

When ranges are used herein, such as for dose ranges, combinations andsubcombinations of ranges (e.g., subranges within the disclosed range),specific embodiments therein are intended to be explicitly included.When the term “about” is used herein, in conjunction with a numericalvalue, it is understood that the value can be in a range of 95% of thevalue to 105% of the value, i.e. the value can be +/−5% of the statedvalue. For example, “about 1 kg” means from 0.95 kg to 1.05 kg.

A greater understanding of the embodiments of the subject invention andof their many advantages may be had from the following examples, givenby way of illustration. The following examples are illustrative of someof the methods, applications, embodiments, and variants of the presentinvention. They are, of course, not to be considered as limiting theinvention. Numerous changes and modifications can be made with respectto embodiments of the invention.

EXAMPLE 1

A HE-UHTC electrode was fabricated by ball-mill mixing raw powders ofHfC, TiC, (TaNb)C to give (TaNbHfTi)C powder and then performing SPS onthe (TaNbHfTi)C powder to give the HE-UHTC electrode. The device shownin FIGS. 7(a) and 7(b) was used to perform an electro-spark depositionprocess to deposit HE-UHTC coatings on steel, INCONEL® (austeniticnickel-chromium-based superalloy), Ti alloy (on a turbine blade), andgraphite substrates. FIG. 1(a) shows images of the HE-UHTC coatings onthe substrates, and FIG. 1(b) shows close-ups of the HE-UHTC coatingsalong the shrouded inner-side of turbine blades with irregular geometry.

FIG. 2(a) shows an X-ray diffraction (XRD) plot for the HE-UHTC coatingon the steel substrate; no phase transformation or oxidation occurredduring the coating process on the steel substrate. FIG. 2(b) shows XRDpatterns for the raw powders (including the (TaNbHfTi)C powder) and theSPS electrode (subscript of “SPS”).

FIG. 3 shows XRD patterns for the SPS HE-UHTC electrode, the graphitesubstrate, and the HE-UHTC coating. No phase transformation or oxidationoccurred during the coating process on the graphite substrate.

FIG. 4 shows DS images of the HE-UHTC coating on the steel substrate, aswell as the elemental mapping (C—K, Ti—K, Mn—K, Ta-M, Hf-M, Nb-L, andFe— K) showing the composition of the HE-UHTC coating on the steelsubstrate. Absence of any oxide phase is reconfirmed with these images.

FIG. 5(a) shows a scanning electron microscope (SEM) image of across-section of the HE-UHTC coating on the steel substrate. The HE-UHTCcoating was ultra-thin and crack-free.

FIGS. 6(a) and 6(b) show SEM images of a cross-section of a thickerHE-UHTC coating on the steel substrate. The stress-relief cracking inthe HE-UHTC coating is due to its increased thickness. This occurs dueto volume change in the rapid solidification of the melted HE-UHTCduring deposition. An optimization of the applied power and speed of therotating applicator can eliminate the stress-relief cracking in theHE-UHTC coating. Though, even the stress-relief cracking in the HE-UHTCcoating show outstanding wear performance (see also FIG. 9 ).

FIG. 8(a) shows an optical image of a Vickers' indent at 25 g force(g=9.8 meters per second squared (m/s²)) on the HE-UHTC coating(hardness of 11 gigaPascals (GPa) to 14 GPa), and FIG. 8(b) shows anoptical image of a Vickers' indent at 25 g force on the steel substrate(hardness of 2.5 GPa-3 GPa). Hardness improved over 4.5 times with theHE-UHTC coating (even at a coating thickness of about 25 μm) compared tothe steel substrate alone.

FIG. 9 shows an optical image of scratch testing that was performed totest wear resistance of the HE-UHTC coating at a constant load of 10Newtons (N) and scratch length of 4 mm, along with COF and acousticemission (AE) data. An optical micrograph of the overall scratch showsless damage on the HE-UHTC side than the steel substrate at a constantload of 10 N. The HE-UHTC coated region has a lower COF (0.40) than thesteel substrate (0.65), which is an indication of an escalation in thetolerance towards wear damage.

EXAMPLE 2

A electrode was fabricated by performing SPS on a MAX® intermetalliccarbide (phase Ti₂AlC) to give a Ti₂AlC electrode. The device shown inFIGS. 7(a) and 7(b) was used to perform an electro-spark depositionprocess to deposit MAX® coatings on steel and INCONEL® substrates.

FIG. 10(a) shows an image of the MAX® coating on a steel substrate, andFIG. 10(b) shows an image of the MAX® coating on the INCONEL® substrate.FIG. 11 shows the XRD pattern for the MAX® coating on the steelsubstrate. No phase transformation or oxidation occurred during thecoating process. FIG. 12 shows EDS images of the MAX® coating on thesteel substrate, as well as the elemental mapping (C—K, Al—K, Ti—K,Fe—K, and Mn—K) showing the composition of the MAX® coating on the steelsubstrate. Absence of any oxide phase is reconfirmed with these images.

FIG. 5(b) shows an SEM image of a cross-section of the MAX® coating onthe steel substrate. The MAX® coating is ultra-thin and crack-free.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

What is claimed is:
 1. A compound, comprising: an electricallyconductive substrate; and a coating of a high-entropy ultra-hightemperature ceramic (HE-UHTC) disposed directly on and in physicalcontact with the substrate, the coating of the HE-UHTC having athickness of less than 100 micrometers (μm).
 2. The compound accordingto claim 1, the substrate being steel, graphite, a nickel-based alloy,or a titanium-based alloy.
 3. The compound according to claim 1, thesubstrate being graphite, C/C, or C/SiC.
 4. The compound according toclaim 1, the HE-UHTC comprising an equimolar composition of at least twoultra-high temperature ceramics (UHTCs).
 5. The compound according toclaim 1, the coating of the HE-UHTC having a thickness in a range offrom 0.1 μm to 80 μm.
 6. The compound according to claim 1, the coatingof the HE-UHTC having a thickness in a range of from 0.1 μm to 50 μm. 7.The compound according to claim 1, the coating of the HE-UHTC having athickness in a range of from 0.1 μm to 30 μm.
 8. The compound accordingto claim 1, the coating of the HE-UHTC having a thickness in a range offrom 0.1 μm to 25 μm.
 9. The compound according to claim 1, the coatingof the HE-UHTC comprising no oxidation or phase transformation.
 10. Thecompound according to claim 1, the coating of the HE-UHTC beingthermally stable up to a temperature of at least 3,000° C.
 11. Thecompound according 1, the HE-UHTC comprising at least one of tantalum(Ta), niobium (Nb), hafnium (Hf), and titanium (Ti).
 12. The compoundaccording to claim 11, the HE-UHTC being a carbide.
 13. The compoundaccording to claim 1, the HE-UHTC being a carbide.
 14. The compoundaccording to claim 1, the HE-UHTC being (TaNbHfTi)C.
 15. A compound,comprising: an electrically conductive substrate; and a coating of ahigh-entropy ultra-high temperature ceramic (HE-UHTC) disposed directlyon and in physical contact with the substrate, the substrate beingsteel, graphite, a nickel-based alloy, a titanium-based alloy, C/C, orC/SiC, the HE-UHTC comprising an equimolar composition of at least twoultra-high temperature ceramics (UHTCs), the coating of the HE-UHTChaving a thickness in a range of from 0.1 micrometers (μm) to 30 μm, thecoating of the HE-UHTC comprising no oxidation or phase transformation,and the coating of the HE-UHTC being thermally stable up to atemperature of at least 2,500° C.
 16. The compound according to claim15, the HE-UHTC comprising at least one of tantalum (Ta), niobium (Nb),hafnium (Hf), and titanium (Ti).
 17. The compound according to claim 16,the HE-UHTC being a carbide.
 18. The compound according to claim 15, theHE-UHTC being (TaNbHfTi)C.